Treatment or isolation of vascular aneurysms or of vessel walls which have been thinned or thickened by disease has traditionally been performed via surgical bypassing with vascular grafts. Shortcomings of this procedure include the morbidity and mortality associated with surgery, long recovery times after surgery, and the high incidence of repeat intervention needed due to limitations of the graft or of the procedure.
Vessels thickened by disease are currently sometimes treated less invasively with intraluminal stents that mechanically hold these vessels open either subsequent to or as an adjunct to a balloon angioplasty procedure. Shortcomings of current stents include the use of highly thrombogenic materials (stainless steels, tantalum, ELGILOY) which are exposed to blood, the general failure of these materials to attract and support functional endothelium, the irregular stent/vessel surface that causes unnatural blood flow patterns, and the mismatch of mechanical compliance and flexibility between the vessel and the stent.
Various attempts have been made to provide a nonthrombogenic blood-carrying conduit. Pinchuk, in U.S. Pat. Nos. 5,019,090, 5,092,887, and 5,163,958, suggests a spring stent which appears to circumferentially and helically wind about as it is finally deployed except, perhaps, at the very end link of the stent. The Pinchuk '958 patent further suggests the use of a pyrolytic carbon layer on the surface of the stent to present a porous surface of improved antithrombogenic properties.
U.S. Pat. No. 5,123,917, to Lee, suggests an expandable vascular graft having a flexible cylindrical inner tubing and a number of “scaffold members” which are expandable, ring-like and provide circumferential rigidity to the graft. The scaffold members are deployed by deforming them beyond their plastic limit using, e.g., an angioplasty balloon.
A variety of stent-graft designs also have been developed to improve upon simple stent configurations. Perhaps the most widely known stent-graft is shown in Ersek, U.S. Pat. No. 3,657,744. Ersek shows a system for deploying expandable, plastically deformable stents of metal mesh having an attached graft through the use of an expansion tool.
Palmaz describes a variety of expandable intraluminal vascular grafts in a sequence of patents: U.S. Pat. Nos. 4,733,665; 4,739,762; 4,776,337; and 5,102,417. The Palmaz '665 patent suggests grafts (which also function as stents) that are expanded using angioplasty balloons. The grafts are variously a wire mesh tube or of a plurality of thin bars fixedly secured to each other. The devices are installed, e.g., using an angioplasty balloon and consequently are not seen to be self-expanding. The Palmaz '762 and '337 patents appear to suggest the use of thin-walled, biologically inert materials on the outer periphery of the earlier-described stents. Finally, the Palmaz '417 patent describes the use of multiple stent sections each flexibly connected to its neighbor.
Rhodes, U.S. Pat. No. 5,122,154, shows an expandable stent-graft made to be expanded using a balloon catheter. The stent is a sequence of ring-like members formed of links spaced apart along the graft. The graft is a sleeve of a material such as an expanded polyfluorocarbon, expanded polytetrafluoroethylene available from W. L. Gore & Associates, Inc. or IMPRA Corporation.
Schatz, U.S. Pat. No. 5,195,984, shows an expandable intraluminal stent and graft related in concept to the Palmaz patents discussed above. Schatz discusses, in addition, the use of flexibly-connecting vascular grafts which contain several of the Palmaz stent rings to allow flexibility of the overall structure in following curving body lumen.
Cragg, “Percutaneous Femoropopliteal Graft Placement”, Radiology, vol. 187, no. 3, pp. 643-648 (1993), shows a stent-graft of a self-expanding, nitinol, zig-zag, helically wound stent having a section of polytetrafluoroethylene tubing sewed to the interior of the stent.
Cragg (European Patent Application 0,556,850) discloses an intraluminal stent made up of a continuous helix of zig-zag wire and having loops at each apex of the zig-zags. Those loops on the adjacent apexes are individually tied together to form diamond-shaped openings among the wires. The stent may be made of a metal such as nitinol (col. 3 lines 15-25 and col. 4, lines 42+), and may be associated with a “polytetrafluoroethylene (PTFE), dacron, or any other suitable biocompatible material”. Those biocompatible materials may be inside the stent (col. 3 lines 52+) or outside the stent (col. 4, lines 6+).
WO93/13825 to Maeda et al. discloses a self-expanding stent having a wire bent into an elongated zig-zag pattern and helically would about a tubular shape interconnected with a filament. A sleeve may be attached to the outer or inner surface of the stent.
PCT application publication WO/95/05132 discloses a stent-graft with a tubular diametrically adjustable stent.
There is a need for an alternate stent-graft construction that exhibits excellent kink resistance and flexibility.